Tenascin C and Anti-Tenascin C Antibodies
Tenascins are a highly conserved family of large multimeric extracellular matrix (ECM) glycoproteins, which is found in vertebrates. Four tenascin paralogues have been identified in mammals, termed tenascin-C, tenascin-R, tenascin-X and tenascin-W. Tenascin family proteins have a common primary structure, comprising N-terminal heptad repeats, epidermal growth factor (EGF)-like repeats, fibronectin type III domain repeats and a C-terminal fibrinogen-like globular domain. Via an N-terminal oligomerization domain, individual subunits assemble into trimers or, as is the case for tenascin-C, even hexamers.
Mammalian tenascin-C monomers typically have 14.5 EGF-like repeats and 8 fibronectin type III domain repeats that are shared by all tenascin-C isoforms. However, up to 9 additional fibronectin type III domain repeats (domains A1 to D) can be independently included or excluded by alternative splicing, giving rise to a large number of tenascin-C isoforms (see e.g. Hsia and Schwarzbauer, J Biol Chem 280, 26641-26644 (2005)).
Tenascin-C is transiently expressed in the developing embryo, but virtually absent from adult tissues. It reappears, however, in tissues undergoing remodeling processes, including certain pathological conditions such as wound healing, inflammation and cancer (reviewed in Chiquet-Ehrismann & Chiquet, J Pathol 200, 488-499 (2003)).
Importantly, tenascin-C is highly expressed in the majority of malignant solid tumors, including tumors of the brain, breast, colon, lung, skin and other organs (reviewed in Orend and Chiquet-Ehrismann, Cancer Letters 244, 143-163 (2006)), where it may be expressed by transformed epithelial cells as well as stromal cells in the tumor microenvironment (Yoshida et al., J Pathol 182, 421-428 (1997), Hanamura et al., Int J Cancer 73, 10-15 (1997)). In particular, the “large isoform” of tenascin-C, containing the alternatively spliced domains A1 to D, is expressed in invasive carcinomas while being nearly undetectable in healthy adult tissues (Borsi et al., Int J Cancer 52, 688-692 (1992), Carnemolla et al., Eur J Biochem 205, 561-567 (1992)). Its expression pattern makes tenascin-C, in particular its alternatively spliced domains, a promising antigen for tumor targeting applications, and accordingly a number of antibodies against several domains of the protein have been developed (see e.g. Brack et al., Clin Cancer Res 12, 3200-3208 (2006) or EP 1 817 345, describing antibodies against the A1 domain of tenascin-C; Silacci et al., Prot Eng Des Sel 19, 471-478 (2006), or EP 1 173 766, describing antibodies against the C domain of tenascin-C; Wang et al., Hybridoma 29, 13-16 (2010), describing an antibody against the D domain of tenascin C; or Balza et al., FEBS 332, 39-43 (1993), describing several antibodies against different domains of human tenascin). Recently, also an antibody recognizing a specific epitope in the A2 domain of human tenascin-C has been described (WO 2009/089998).
Antibody Glycosylation
The oligosaccharide component can significantly affect properties relevant to the efficacy of a therapeutic glycoprotein, including physical stability, resistance to protease attack, interactions with the immune system, pharmacokinetics, and specific biological activity. Such properties may depend not only on the presence or absence, but also on the specific structures, of oligosaccharides. Some generalizations between oligosaccharide structure and glycoprotein function can be made. For example, certain oligosaccharide structures mediate rapid clearance of the glycoprotein from the bloodstream through interactions with specific carbohydrate binding proteins, while others can be bound by antibodies and trigger undesired immune reactions (Jenkins et al., Nature Biotechnol 14, 975-81 (1996)).
IgG1 type antibodies, the most commonly used antibodies in cancer immunotherapy, are glycoproteins that have a conserved N-linked glycosylation site at Asn 297 in each CH2 domain. The two complex biantennary oligosaccharides attached to Asn 297 are buried between the CH2 domains, forming extensive contacts with the polypeptide backbone, and their presence is essential for the antibody to mediate effector functions such as antibody dependent cell-mediated cytotoxicity (ADCC) (Lifely et al., Glycobiology 5, 813-822 (1995); Jefferis et al., Immunol Rev 163, 59-76 (1998); Wright and Morrison, Trends Biotechnol 15, 26-32 (1997)). Protein engineering studies have shown that FcγRs interact with the lower hinge region of the IgG CH2 domain. Lund et al., J. Immunol. 157:4963-69 (1996). However, FcγR binding also requires the presence of the oligosaccharides in the CH2 region. Lund et al., J. Immunol. 157:4963-69 (1996); Wright and Morrison, Trends Biotech. 15:26-31 (1997), suggesting that either oligosaccharide and polypeptide both directly contribute to the interaction site or that the oligosaccharide is required to maintain an active CH2 polypeptide conformation. Modification of the oligosaccharide structure can therefore be explored as a means to increase the affinity of the interaction between IgG1 and FcγR, and to increase ADCC activity of IgG1s.
A way to obtain large increases in the potency of monoclonal antibodies, is to enhance their natural, cell-mediated effector functions by engineering their oligosaccharide component as described in Umaña et al., Nat Biotechnol 17, 176-180 (1999) and U.S. Pat. No. 6,602,684 (WO 99/54342), the contents of which are hereby incorporated by reference in their entirety. Umaña et al. showed that overexpression of β(1,4)-N-acetylglucosaminyltransferase III (GnTIII), a glycosyltransferase catalyzing the formation of bisected oligosaccharides, in Chinese hamster ovary (CHO) cells significantly increases the in vitro ADCC activity of antibodies produced in those cells. Overexpression of GnTIII in production cell lines leads to antibodies enriched in bisected oligosaccharides, which are generally also non-fucosylated and of the hybrid type. If in addition to GnTIII, mannosidase II (ManII) is overexpressed in production cell lines, antibodies enriched in bisected, non-fucosylated oligosaccharides of the complex type are obtained (Ferrara et al., Biotechn Bioeng 93, 851-861 (2006)). Both types of antibodies show strongly enhanced ADCC, as compared to antibodies with unmodified glycans, but only antibodies in which the majority of the N-glycans are of the complex type are able to induce significant complement-dependent cytotoxicity (Ferrara et al., Biotechn Bioeng 93, 851-861 (2006)). Alterations in the composition of the Asn 297 carbohydrate or its elimination also affect binding of the antibody Fc-domain to Fcγ-receptor (FcγR) and complement C1q protein, which is important for ADCC and CDC, respectively (Umaña et al., Nat Biotechnol 17, 176-180 (1999); Davies et al., Biotechnol Bioeng 74, 288-294 (2001); Mimura et al., J Biol Chem 276, 45539-45547 (2001); Radaev et al., J Biol Chem 276, 16478-16483 (2001); Shields et al., J Biol Chem 276, 6591-6604 (2001); Shields et al., J Biol Chem 277, 26733-26740 (2002); Simmons et al., J Immunol Methods 263, 133-147 (2002)).